Leveraging temporal locality to link files together and bypass accessing a central inode list

ABSTRACT

A computer-implemented method, according to one embodiment, includes: receiving an access request for data in a first block of storage space in memory, and returning the data in the first block of storage space in response to the access request. An identifier at an end of the data in the first block of storage space is also located, and pointers included in a trailer appended to the identifier are used to identify additional blocks of storage space which include data having temporal locality with the data in the first block of storage space. The data in each of the identified additional blocks of storage space is further prepared for use.

BACKGROUND

The present invention relates to data storage systems, and morespecifically, this invention relates to leveraging temporal localitybetween files in order to avoid accessing a central inode list.

The continued increase of resilience for filesystems is an issue whichis addressed on ongoing basis. Most filesystems initially start as asuperblock which is located at an arbitrary address in a logical unitnumber (LUN), volume, logical disk, etc. From the superblock, astructure is built which ultimately becomes the filesystem. Files (e.g.,unique groupings of data) stored on the filesystem are typicallyseparated into a number of blocks which are spread across the persistentstorage space of memory in order to achieve even distribution, e.g., forperformance reasons. Thus, in order to describe each of these blocks andkeep track of where they are located in the persistent storage space, astructure called a central inode list is used. This inode listidentifies where the logical block addresses (LBAs) that constitute thevarious portions (e.g., blocks) of a given file are located in thememory space, and how these correlate to the corresponding locations inthe persistent storage space. Accordingly, each file has an inode whichis stored in one or more arrays depending on the architecture.

However, as file systems grow and become larger, multiple processesand/or threads are allowed to simultaneously access a single inode list.Accordingly, the inode list can become a performance bottleneck andconsume valuable system resources, including but not limited to memoryand central processing units (CPUs). Moreover, lease and lock requestsare implemented per inode in order to access files which adds anotherlayer of complexity to the process of accessing data stored in memory.

SUMMARY

A computer-implemented method, according to one embodiment, includes:receiving an access request for data in a first block of storage spacein memory, and returning the data in the first block of storage space inresponse to the access request. An identifier at an end of the data inthe first block of storage space is also located, and pointers includedin a trailer appended to the identifier are used to identify additionalblocks of storage space which include data having temporal locality withthe data in the first block of storage space. The data in each of theidentified additional blocks of storage space is further prepared foruse.

A computer program product, according to another embodiment, includes acomputer readable storage medium having program instructions embodiedtherewith. The computer readable storage medium is not a transitorysignal per se. Moreover, the program instructions are readable and/orexecutable by a processor to cause the processor to perform a methodwhich includes: receiving, by the processor, an access request for datain a first block of storage space in memory; and returning, by theprocessor, the data in the first block of storage space in response tothe access request. An identifier at an end of the data in the firstblock of storage space is located, by the processor; and pointersincluded in a trailer appended to the identifier are used, by theprocessor, to identify additional blocks of storage space which includedata having temporal locality with the data in the first block ofstorage space. The data in each of the identified additional blocks ofstorage space is further prepared, by the processor, for use.

A system, according to yet another embodiment, includes: a processor;and logic integrated with the processor, executable by the processor, orintegrated with and executable by the processor. The logic is configuredto: receive, by the processor, an access request for data in a firstblock of storage space in memory; and return, by the processor, the datain the first block of storage space in response to the access request.An identifier at an end of the data in the first block of storage spaceis located, by the processor; and pointers included in a trailerappended to the identifier are also used, by the processor, to identifyadditional blocks of storage space which include data having temporallocality with the data in the first block of storage space. The data ineach of the identified additional blocks of storage space are furtherprepared, by the processor, for use.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a network architecture, in accordance with one embodiment.

FIG. 2 is a representative hardware environment that may be associatedwith the servers and/or clients of FIG. 1, in accordance with oneembodiment.

FIG. 3 is a tiered data storage system in accordance with oneembodiment.

FIG. 4A is a flowchart of a method in accordance with one embodiment.

FIG. 4B is a flowchart of a method in accordance with anotherembodiment.

FIG. 4C is a flowchart of a method in accordance with anotherembodiment.

FIG. 5 is a flowchart of a method in accordance with another embodiment.

FIG. 6A is a flowchart of a method in accordance with yet anotherembodiment.

FIG. 6B is a flowchart of sub-processes for one of the operations in themethod of FIG. 6A, in accordance with one embodiment.

FIG. 6C is a flowchart of sub-processes for one of the operations in themethod of FIG. 6A, in accordance with one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

The following description discloses several preferred embodiments ofsystems, methods and computer program products for utilizing adistributed copy of metadata, in conjunction with pointers to performdata access operations. The distributed metadata is resilient againstdata loss and does not consume otherwise usable storage space. Moreover,the pointers are able to link files which have a level of temporallocality with each other. Thus, the various improvements to the dataaccess process achieved by the approaches included herein come at nostorage cost which is significantly desirable, particularly in view ofthe shortcomings experienced by conventional implementations, e.g., aswill be described in further detail below.

In one general embodiment, a computer-implemented method includes:receiving an access request for data in a first block of storage spacein memory, and returning the data in the first block of storage space inresponse to the access request. An identifier at an end of the data inthe first block of storage space is also located, and pointers includedin a trailer appended to the identifier are used to identify additionalblocks of storage space which include data having temporal locality withthe data in the first block of storage space. The data in each of theidentified additional blocks of storage space is further prepared foruse.

In another general embodiment, a computer program product includes acomputer readable storage medium having program instructions embodiedtherewith. The computer readable storage medium is not a transitorysignal per se. Moreover, the program instructions are readable and/orexecutable by a processor to cause the processor to perform a methodwhich includes: receiving, by the processor, an access request for datain a first block of storage space in memory; and returning, by theprocessor, the data in the first block of storage space in response tothe access request. An identifier at an end of the data in the firstblock of storage space is located, by the processor; and pointersincluded in a trailer appended to the identifier are used, by theprocessor, to identify additional blocks of storage space which includedata having temporal locality with the data in the first block ofstorage space. The data in each of the identified additional blocks ofstorage space is further prepared, by the processor, for use.

In yet another general embodiment, a system includes: a processor; andlogic integrated with the processor, executable by the processor, orintegrated with and executable by the processor. The logic is configuredto: receive, by the processor, an access request for data in a firstblock of storage space in memory; and return, by the processor, the datain the first block of storage space in response to the access request.An identifier at an end of the data in the first block of storage spaceis located, by the processor; and pointers included in a trailerappended to the identifier are also used, by the processor, to identifyadditional blocks of storage space which include data having temporallocality with the data in the first block of storage space. The data ineach of the identified additional blocks of storage space are furtherprepared, by the processor, for use.

FIG. 1 illustrates an architecture 100, in accordance with oneembodiment. As shown in FIG. 1, a plurality of remote networks 102 areprovided including a first remote network 104 and a second remotenetwork 106. A gateway 101 may be coupled between the remote networks102 and a proximate network 108. In the context of the presentarchitecture 100, the networks 104, 106 may each take any formincluding, but not limited to a local area network (LAN), a wide areanetwork (WAN) such as the Internet, public switched telephone network(PSTN), internal telephone network, etc.

In use, the gateway 101 serves as an entrance point from the remotenetworks 102 to the proximate network 108. As such, the gateway 101 mayfunction as a router, which is capable of directing a given packet ofdata that arrives at the gateway 101, and a switch, which furnishes theactual path in and out of the gateway 101 for a given packet.

Further included is at least one data server 114 coupled to theproximate network 108, and which is accessible from the remote networks102 via the gateway 101. It should be noted that the data server(s) 114may include any type of computing device/groupware. Coupled to each dataserver 114 is a plurality of user devices 116. User devices 116 may alsobe connected directly through one of the networks 104, 106, 108. Suchuser devices 116 may include a desktop computer, lap-top computer,hand-held computer, printer or any other type of logic. It should benoted that a user device 111 may also be directly coupled to any of thenetworks, in one approach.

A peripheral 120 or series of peripherals 120, e.g., facsimile machines,printers, networked and/or local storage units or systems, etc., may becoupled to one or more of the networks 104, 106, 108. It should be notedthat databases and/or additional components may be utilized with, orintegrated into, any type of network element coupled to the networks104, 106, 108. In the context of the present description, a networkelement may refer to any component of a network.

According to some approaches, methods and systems described herein maybe implemented with and/or on virtual systems and/or systems whichemulate one or more other systems, such as a UNIX system which emulatesan IBM z/OS environment, a UNIX system which virtually hosts a MICROSOFTWINDOWS environment, a MICROSOFT WINDOWS system which emulates an IBMz/OS environment, etc. This virtualization and/or emulation may beenhanced through the use of VMWARE software, in some approaches.

In more approaches, one or more networks 104, 106, 108, may represent acluster of systems commonly referred to as a “cloud.” In cloudcomputing, shared resources, such as processing power, peripherals,software, data, servers, etc., are provided to any system in the cloudin an on-demand relationship, thereby allowing access and distributionof services across many computing systems. Cloud computing typicallyinvolves an Internet connection between the systems operating in thecloud, but other techniques of connecting the systems may also be used.

FIG. 2 shows a representative hardware environment associated with auser device 116 and/or server 114 of FIG. 1, in accordance with oneapproach. Such figure illustrates a typical hardware configuration of aworkstation having a central processing unit 210, such as amicroprocessor, and a number of other units interconnected via a systembus 212.

The workstation shown in FIG. 2 includes a Random Access Memory (RAM)214, Read Only Memory (ROM) 216, an input/output (I/O) adapter 218 forconnecting peripheral devices such as disk storage units 220 to the bus212, a user interface adapter 222 for connecting a keyboard 224, a mouse226, a speaker 228, a microphone 232, and/or other user interfacedevices such as a touch screen and a digital camera (not shown) to thebus 212, communication adapter 234 for connecting the workstation to acommunication network 235 (e.g., a data processing network) and adisplay adapter 236 for connecting the bus 212 to a display device 238.

The workstation may have resident thereon an operating system such asthe Microsoft Windows® Operating System (OS), a MAC OS, a UNIX OS, etc.It will be appreciated that a preferred approach may also be implementedon platforms and operating systems other than those mentioned. Apreferred approach is written using eXtensible Markup Language (XML), C,and/or C++ language, or other programming languages, along with anobject oriented programming methodology. Object oriented programming(OOP), which has become increasingly used to develop complexapplications, may be used.

Now referring to FIG. 3, a storage system 300 is shown according to oneembodiment. Note that some of the elements shown in FIG. 3 may beimplemented as hardware and/or software, according to variousapproaches. The storage system 300 may include a storage system manager312 for communicating with a plurality of media and/or drives on atleast one higher storage tier 302 and at least one lower storage tier306. The higher storage tier(s) 302 preferably may include one or morerandom access and/or direct access media 304, such as hard disks in harddisk drives (HDDs), nonvolatile memory (NVM), solid state memory insolid state drives (SSDs), flash memory, SSD arrays, flash memoryarrays, etc., and/or others noted herein or known in the art. The lowerstorage tier(s) 306 may preferably include one or more lower performingstorage media 308, including sequential access media such as magnetictape in tape drives and/or optical media, slower accessing HDDs, sloweraccessing SSDs, etc., and/or others noted herein or known in the art.One or more additional storage tiers 316 may include any combination ofstorage memory media as desired by a designer of the system 300. Also,any of the higher storage tiers 302 and/or the lower storage tiers 306may include some combination of storage devices and/or storage media.

The storage system manager 312 may communicate with the drives and/orstorage media 304, 308 on the higher storage tier(s) 302 and lowerstorage tier(s) 306 through a network 310, such as a storage areanetwork (SAN), as shown in FIG. 3, or some other suitable network type.The storage system manager 312 may also communicate with one or morehost systems (not shown) through a host interface 314, which may or maynot be a part of the storage system manager 312. The storage systemmanager 312 and/or any other component of the storage system 300 may beimplemented in hardware and/or software, and may make use of a processor(not shown) for executing commands of a type known in the art, such as aCPU, a field programmable gate array (FPGA), an application specificintegrated circuit (ASIC), etc. Of course, any arrangement of a storagesystem may be used, as will be apparent to those of skill in the artupon reading the present description.

In more approaches, the storage system 300 may include any number ofdata storage tiers, and may include the same or different storage memorymedia within each storage tier. For example, each data storage tier mayinclude the same type of storage memory media, such as HDDs, SSDs,sequential access media (tape in tape drives, optical disc in opticaldisc drives, etc.), direct access media (CD-ROM, DVD-ROM, etc.), or anycombination of media storage types. In one such configuration, a higherstorage tier 302, may include a majority of SSD storage media forstoring data in a higher performing storage environment, and remainingstorage tiers, including lower storage tier 306 and additional storagetiers 316 may include any combination of SSDs, HDDs, tape drives, etc.,for storing data in a lower performing storage environment. In this way,more frequently accessed data, data having a higher priority, dataneeding to be accessed more quickly, etc., may be stored to the higherstorage tier 302, while data not having one of these attributes may bestored to the additional storage tiers 316, including lower storage tier306. Of course, one of skill in the art, upon reading the presentdescriptions, may devise many other combinations of storage media typesto implement into different storage schemes, according to the approachespresented herein.

According to some approaches, the storage system (such as 300) mayinclude logic configured to receive a request to open a data set, logicconfigured to determine if the requested data set is stored to a lowerstorage tier 306 of a tiered data storage system 300 in multipleassociated portions, logic configured to move each associated portion ofthe requested data set to a higher storage tier 302 of the tiered datastorage system 300, and logic configured to assemble the requested dataset on the higher storage tier 302 of the tiered data storage system 300from the associated portions.

Of course, this logic may be implemented as a method on any deviceand/or system or as a computer program product, according to variousapproaches.

As previously mentioned, the continued increase of resilience forfilesystems in the face of storage-related disasters is an issue whichis addressed on ongoing basis. Particularly, situations in which acentral inode list is lost has traditionally proven to be a significantissue in terms of retaining data and maintaining operation of thestorage system as a whole. Losing the central inode list undesirablycauses the entire filesystem to essentially become useless, as there isno way of identifying where each file begins, much less where each ofthe various blocks that belong to that file reside throughout thememory. In other words, without the central inode list, the informationstored in memory essentially becomes an indecipherable string of logical“1s” and “0s”.

Accordingly, conventional implementations have attempted to maintain aredundant copy of the central inode list, e.g., such that it may be usedin situations where the central inode list is lost. While these attemptsto replicate the inode list and its indirect blocks is plausible, doingso would cause a significant detriment to system performance andintegrity, as multiple copies have to be maintained. Furthermore, theseconventional strategies have proven to be impractical options, as theredundant copies of the central inode list consume an undesirably largeamount of storage space otherwise available for user data. Thus,conventional technology has been forced to choose between poor dataretention rates and significant reductions to storage capacity.

It follows that a data storage scheme which is able to maintain dataretention in the face of inode list failure without sacrificing storagecapacity in doing so is desirable.

In sharp contrast to the aforementioned shortcomings experienced byconventional implementations, various ones of the approaches includedherein are able to establish and maintain a distributed inode list insuch a manner that does not consume otherwise usable storage space,e.g., as will be described in further detail below.

Referring now to FIG. 4A, a flowchart of a method 400 for creating adistributed inode list which does not consume any otherwise usablestorage space is shown according to one embodiment. The method 400 maybe performed in accordance with the present invention in any of theenvironments depicted in FIGS. 1-3, among others, in various approaches.Of course, more or less operations than those specifically described inFIG. 4A may be included in method 400, as would be understood by one ofskill in the art upon reading the present descriptions. Moreover, someor all of the operations of the method 400 may be combined with some orall operations of the other figures, e.g., FIGS. 4B-5, in anycombination in various embodiments.

Each of the steps of the method 400 may be performed by any suitablecomponent of the operating environment. For example, in variousapproaches, the method 400 may be partially or entirely performed by acontroller, a processor, a computer, etc., or some other device havingone or more processors therein. Furthermore, the controller, processor,computer, etc., used to perform various ones of the processes in method400 is electrically coupled to a memory in preferred approaches. Thus,in some approaches, method 400 is a computer-implemented method.Moreover, the terms computer, processor and controller may be usedinterchangeably with regards to any of the approaches herein, suchcomponents being considered equivalents in the many various permutationsof the present invention.

Moreover, for those approaches having a processor, the processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method400. Illustrative processors include, but are not limited to, a centralprocessing unit (CPU), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), etc., combinationsthereof, or any other suitable computing device known in the art.

As shown in FIG. 4A, operation 402 of method 400 includes receiving awrite request which includes data. The data included in the writerequest typically corresponds to a specific file (e.g., unique groupingof data). Accordingly, operation 404 includes allocating an inode entryin a central inode list correlated with the file which corresponds tothe data included in the write request. As previously mentioned, acentral inode list is used to store metadata which describes each of theblocks of storage space in memory, including the location of each of theblocks in the persistent storage space, as well as the LBAscorresponding thereto in some approaches. It follows that each file hasan inode entry corresponding thereto, which is stored in the centralinode list. However, it should be noted that in some approaches thewrite request received in operation 402 corresponds to an alreadyexisting file. Thus, operation 404 may simply include updating analready existing inode entry in the central inode list in someapproaches.

Moreover, the process of allocating (e.g., “creating”) inodes, and evenif they are even allocated in the first case, depends on the specificfile system. For instance, some file systems (e.g., ext3) create all ofinode entries when the file system is created, thereby resulting in afixed number of inodes. As a result, in some approaches the file systemhas a fixed number of files that can be stored therein.

According to some approaches, which are in no way intended to limit theinvention, the central inode list is stored in a designated storagelocation of the main memory. As mentioned above, the inode list ispre-allocated in some approaches such that the process of allocating aninode entry in a central inode list is actually performed by selectingan unused inode entry from the pre-allocated array of available entriesand marking it as being used. Accordingly, each inode entry is lockedfrom being reused, overwritten, taken, etc. by other operations.

The metadata which is included in each of the inode entries in thecentral inode list varies depending on the given approach. For instance,in some approaches each of the entries in a central inode list includemetadata which specifies the last time the respective file was accessed,the last time the respective file was modified, the size of therespective file, the name of the respective file, etc., or any otherdesired metadata.

The data included in the received write request makes up a full fileand/or a portion thereof depending on the approach. Accordingly,operation 406 further includes allocating at least one block of storagespace to store the data (e.g., file) received. As mentioned above, thecontroller, processor, computer, etc., used to perform various ones ofthe processes in method 400 is electrically coupled to a memory in someapproaches. With respect to the present description, the “memory” isintended to refer to the persistent storage space of any type of datastorage medium, e.g., such as SSD, HDD, Flash, etc. Accordingly, thememory includes multiple blocks of storage space, each of which has anabout equal data storage capacity.

The number of blocks of storage space allocated in operation 406 dependson the amount of data received in the write request (e.g., a size of thefile) and/or whether a Redundant Array of Independent Disks (RAID)scheme is implemented. For example, more than one block of storage spaceis allocated in operation 406 if the amount of data received is greaterthan the storage capacity of a single block of storage space. Accordingto another example, a RAID scheme identifying a specific distribution ofthe data may specify that more than one block of storage space be usedto store the data, irrespective of the storage capacity the blocks mayhave.

In addition to allocating an inode entry and storing metadata, the dataitself is actually stored in the one or more blocks of storage space.Accordingly, operation 408 includes sending one or more instructions towrite the data to the at least one block of storage space. According tosome approaches, the write instructions are sent to an existing file,e.g., such that one or more of the blocks storing the data thereof areoverwritten.

Depending on the processing device used to perform the various processesof method 400 and/or the implementation of this processing device,operation 408 may include sending the one or more instructions todifferent locations. For example, in some approaches the variousprocesses of method 400 are performed by a central controller.Accordingly, the central controller may send the one or moreinstructions to write the data to the at least one block of storagespace to a storage controller. However, in other approaches method 400is performed by a storage controller, in which case the one or moreinstructions to write the data to the at least one block of storagespace are sent directly to a writing component of the memory, e.g., suchas a magnetic read/write head of an HDD, a memory I/O unit of aFlash-based SSD, etc.

With continued reference to FIG. 4A, decision 410 includes determiningwhether the data at an end of the corresponding file fills a thresholdamount of a last block of storage space allocated to store the data. Inother words, decision 410 includes determining whether a last one of thepages included in a last block of storage space allocated to store thegiven file has been filled to, or above, a threshold as a result of thedata being written thereto. In a filesystem, each file is allocated tochunks of blocks, these chunks also being referred to as pages. However,the granularity of the pages with respect to the files typicallyprevents each of the various blocks from being filled entirely. In otherwords, the process of adding a file to a filesystem rarely produces oneor more blocks which are filled to their capacity. It follows that inmany situations, the final page and/or the final block of storage spaceused to store the data corresponding to a given file has a “tail” regionof unused storage space which follows an end of the data stored therein.Moreover, this unused storage space in the tail region of the last blockfound at the end of a given file are preferably used in various ones ofthe embodiments herein to store metadata (e.g., such as a copy of thecorresponding inode entry), thereby improving resourcefulness androbustness of the storage system without sacrificing storage capacity.

According to preferred approaches, the threshold is set such that a lastblock storing an amount of data which is at or below the threshold has aremaining amount of available storage space which is sufficient to storea copy of an inode entry therein. It follows that the threshold may bepredetermined, set by a user, updated in real time, etc., depending onthe desired approach. Moreover, the threshold may be represented as apercentage of the block's storage capacity (e.g., 80%, 85%, 90%, 93%,etc.), a specified amount of data, etc., depending on the approach. Itshould also be noted that “fills a threshold” is in no way intended tolimit the invention. Rather than determining whether the data in a givenblock fills a threshold amount of the storage space included therein,equivalent determinations may be made, e.g., as to whether the amount ofdata in the given block is within a predetermined range, outside apredetermined range, below a threshold, etc., depending on the desiredapproach.

According to a specific example, which is in no way intended to limitthe invention, decision 410 is performed by determining whether theamount of data (e.g., size of the file) received in operation 402 isless than the size of one of the blocks multiplied by the number ofblocks allocated for the corresponding file. In other words, decision410 is performed in some approaches by determining whether the amount ofdata being stored in the one or more allocated blocks is less than thecombined storage capacity of the one or more allocated blocks.

It follows that determining the data does not fill a threshold amount ofa last block at an end of the file indicates the given block has a tailregion of unused storage space which begins at an end of the data thatis stored therein. Thus, method 400 proceeds to operation 412 inresponse to determining that the data does not fill a threshold amountof the last allocated block of storage space. There, operation 412includes sending one or more instructions to create an identifier at anend of the data stored in the last block of storage space. Thisidentifier (which is also referred to herein as a “magic string”) servesas a way of clearly indicating an end of the data (and an end of thefile itself) stored in the block, even in disaster situations where thecentral inode list is inaccessible, e.g., as will be described infurther detail below. Thus, the identifier preferably includes a uniquestring of logical “1s” and “0s” which are easily distinguishable from aremainder of the data stored in the memory.

Furthermore, operation 414 includes sending one or more instructions tostore a copy of the inode entry allocated (or updated) in operation 404,after the identifier in the unused tail region of the last block ofstorage space. The identifier (e.g., magic string) thereby serves as aboundary separating the data from the copy of the inode entry in thefinal block of storage space. Moreover, implementing the identifiercauses a beginning of the inode entry to be easily identifiable andtherefore distinguishable from the data, e.g., as mentioned above.

Again, the inode entry copies stored in the tail regions of blocksthroughout memory serve as a distributed backup of the central inodelist in preferred approaches. The metadata included in each of theseinode entry copies is therefore used in some approaches to reconstructthe central inode list, or at least a portion thereof, e.g., insituations where the central inode list is lost or otherwiseinaccessible. However, the amount of unused storage space available ineach of the blocks is limited in some cases. Thus, in order to increasethe number files having a last block with an adequate amount of unusedstorage space to store an identifier and a corresponding copy of aninode entry, the storage footprint of each of the inode entry copies maybe reduced. This reduced footprint is achieved in some approaches bydecreasing the amount of metadata included in the copy of an inode entrywith respect to the amount of metadata included in the inode entryitself. In other words, the metadata included in the copy of an inodeentry is reduced in some approaches to only include the metadata whichwould be used in reconstructing a central inode list.

For instance, superfluous portions of the metadata in a given inode listentry, e.g., such as metadata which indicates the last time acorresponding file was accessed, the last time a corresponding file wasmodified, permission information, etc., may be selectively removed whenforming the copy of the given inode list entry. According to an example,which is in no way intended to limit the invention, the copy of thegiven inode list entry may only include the head of the correspondingmetadata list. Accordingly, the indirect blocks are not replicated, butrather rely on being sufficiently distributed across the storage space,and as such, are not likely to be lost like the central inode-list. Insome approaches, the metadata which is actually included in each ofthese condensed inode entry copies may be predetermined, specified by auser, adjusted based on the amount of unused storage space in acorresponding block, etc. Certain metadata may actually be added to eachof the copies of the inode list entries, e.g., such as a user-readablename of the corresponding file, e.g., as would be appreciated by oneskilled in the art after reading the present description.

As alluded to above, the tail region of unused storage space in a blockis otherwise not utilized during the data storage process. Thus, storingcopies of inode entries in these tail regions as described herein has nodetrimental impact on the overall storage capacity of the memory.Furthermore, these tail regions of unused storage space are spreadacross the memory in a distributed manner. Thus, the inode entry copiesstored therein are also distributed across memory in a manner whichincreases overall retention. Even in the event that the central inodelist becomes inaccessible, the approaches included herein remainresistant to a total loss of the information included in the inode list.For example, while some blocks of storage space in memory may fail orotherwise become inaccessible, the inode entry copies included thereinare only a small portion of the total number of inode entry copies whichare distributed across the various blocks of storage space.

As a result, the storage architecture achieved as a result ofimplementing method 400 is able to maintain a distributed copy of thecentral inode list which is resilient and which does not consumeotherwise usable storage space. In other words, the various improvementsachieved by the various approaches herein come at no storage cost whichis significantly desirable.

It should also be noted that although operation 414 is illustrated inFIG. 4A as being performed following operation 404, in other approachesthe copy of an inode entry may be stored in a block of storage spacebefore a corresponding entry is allocated (e.g., created) in the centralinode list.

Returning to decision 410, method 400 proceeds to operation 416 inresponse to determining that the data does fill a threshold amount ofthe last block of storage space. In other words, method 400 proceeds tooperation 416 in response to determining that the last block of storagespace allocated to store the data of a file is filled to a point that anidentifier and/or a copy of an inode entry is unable to be storedtherein. Looking to operation 416, an alternate/another last block/pageof storage space at an end of another file which includes an amount ofunused storage sufficient to store the copy of the inode entry isidentified. With respect to the present description, thealternate/another file's last block/page of storage space is one whichhas enough vacant (unused) space to host more than its own meta data,and thereby serve as a repository for other copies of inode entries. Inother words, although the last block used to store the data in a file isfilled at or past a threshold capacity, another “last block” at an endof a different file may have a sufficient amount of unused storage spaceto store the copy of the inode entry in some approaches. For example,the block of storage space at an end of a file previously stored inmemory includes an amount of unused storage space (e.g., a tail region)which is able to store the copy of the inode entry. In some approaches,this alternate/another file's last block/page of storage space is usedto store an additional copy of the inode entry which corresponds to animportant file which may be unable to accommodate its own meta-data inthe tail region thereof, e.g., as will be described in further detailbelow.

This alternate last file block/page of storage space is identified insome approaches by simply comparing an amount of data included in thecopy of the inode entry with the amount of unused storage space in thelast block of various other files. Moreover, a last block having agreatest amount of unused storage space, having an amount of unusedstorage space which most closely matches the size of the amount of dataincluded in the copy of the inode entry, which does not already includea copy of an inode entry stored therein, etc. may be identified (e.g.,selected) as the alternate last file block/page in operation 416. Itfollows that the location, contents, configuration, etc. of thealternate last file block/page of storage space varies depending on theapproach.

However, it should be noted that in some approaches the available spaceat the end of alternate last file blocks/pages of storage space ispreserved, e.g., to store copies of inode entries which correspond tothe respective files. Accordingly, although not depicted in FIG. 4A,some approaches involve determining whether storing the copy of theinode in an alternate last file block/page is desirable beforeproceeding to operation 416. In such approaches, method 400 proceeds tooperation 416 in response to determining that storing the copy of theinode in an alternate last file block/page is desirable. However, inresponse to determining that storing the copy of the inode in analternate last file block/page is not desirable, method 400 proceedsdirectly to operation 442 whereby method 400 may end.

Referring still to FIG. 4A, operation 418 includes sending one or moreinstructions to create an identifier (e.g., magic string) at an end ofthe data already stored in the identified alternate last file block/pageof storage space. However, in some approaches the alternate last fileblock/page of storage space may already have an identifier includedtherein. According to one example, the alternate last file block/page ofstorage space identified in operation 416 already includes an identifieras well as a copy of another inode entry stored therein. Accordingly,operation 418 is skipped over (not performed) in some approaches.

Moving to operation 420, method 400 includes sending one or moreinstructions to store the copy of the inode entry after an identifier inthe alternate last file block/page of storage space. Any of theapproaches described above with respect to operation 414 may beimplemented in order to perform operation 420. Accordingly, thepreviously mentioned improvements are also achieved as a result ofstoring the copy of the inode entry in an alternate last file block/pageof storage space.

Furthermore, optional operation 422 includes sending one or moreinstructions to store a timestamp which corresponds to the copy of theinode entry. Approaches in which a tail region at the end of a file isable to store the inode information of more than one different fileutilize timestamps in order to distinguish between the different inodeentry copies. For instance, more than one copy of the same inodeinformation can be stored in different blocks of storage space in someapproaches. Thus, a timestamp is used to determine which of the copiesis most recent and therefore provides a most accurate representation ofthe corresponding inode entry. Again, timestamps are relevant if tailsof other files can store the inode information of multiple files.Accordingly, operation 422 is not performed in some approaches.

However, it should be noted that in some approaches, a copy of a giveninode entry for a file is not implemented in any of the blocks ofstorage space in response to determining that the block of storage spacewhich corresponds to the given inode entry is filled to or above athreshold amount. The process of storing the copy of an inode entry inan alternate last file block/page of storage space causes the number ofblocks allocated for the file to increase by one, which is in turnreflected in the central inode list. Thus, in order to avoid any impacton the central inode list, operations 416, 418, 420 and 422 are notperformed and the copy of the inode entry is not added in an alternatelast file block/page of storage space in some approaches, e.g., as wouldbe appreciated by one skilled in the art after reading the presentdescription.

Referring still to FIG. 4A, method 400 is illustrated as proceeding tooperation 424 from both operation 414 as well as operation 422. Uponreaching operation 424, method 400 ends in some approaches. However, itshould be noted that although method 400 may end upon reaching operation424, any one or more of the processes included in method 400 may berepeated in order to process subsequently received write requests.However, in other approaches method 400 includes performing additionalprocesses which correspond to different circumstances, some of which mayarise during implementation. For instance, looking to FIG. 4B, processesof a method 430 which may be used to supplement method 400 areillustrated in accordance with an exemplary approach, one or more ofwhich may be implemented following the performance of operation 414and/or operation 422, e.g., rather than proceeding to operation 424 andending method 400. However, it should be noted that the supplementalprocesses of FIG. 4B are illustrated in accordance with one embodimentwhich is in no way intended to limit the invention.

As shown, decision 432 involves determining whether the data included inthe write request received in operation 402 has a high priorityassociated therewith. Sometimes specific data (e.g., files) is ofparticular importance to a user, the successful operation of afilesystem, a given application, etc. The importance of such data isidentified in some approaches by assigning a priority to the data, suchthat it may be distinguished from other data having less importance. Thepriority assigned to different data may further be distinguished byincorporating different priority levels. For example, data having amedium priority may be more important than data having a low priority,but less important than data having a high priority.

It is desirable in some approaches that data having a sufficiently highpriority is afforded additional data retention measures. In other words,data which has a high priority is given added protection to avoid lossas a result of a disaster situation, unintended erasure, memory failure,etc. For example, a second copy of the data determined as having a highpriority may be stored for added redundancy. Thus, in response todetermining that the data included in the received write request has ahigh priority associated therewith, method 400 proceeds to operation434. There, operation 434 includes identifying an alternate last fileblock/page of storage space at an end of another file which includes anamount of unused storage sufficient to store a second copy of the inodeentry. As mentioned above, the “last block” at an end of other files mayhave a sufficient amount of unused storage space to store the copy of aninode entry which corresponds to a different file than that which thedata stored therein represents. For example, the block of storage spaceat an end of a file previously stored in memory includes an amount ofunused storage space (e.g., a tail region) which is able to store asecond copy of the inode entry.

Upon being implemented in memory, this second copy of the inode entryserves as a backup to the other copy previously stored in the tailregion of another last block of storage space. Thus, even if the centralinode list as well as one of the copies of the inode entry are lost, theother remaining copy of the inode entry may be used to reconstruct thecorresponding inode entry.

Operation 436 further includes sending one or more instructions tocreate an identifier (e.g., magic string) at an end of the data alreadystored in the alternate last block of storage space identified inoperation 434. As mentioned above, in some approaches the identifiedalternate last file block/page of storage space may already have anidentifier included therein. According to one example, the alternatelast file block/page of storage space identified in operation 434already includes an identifier and possibly a copy of another inodeentry stored therein. Accordingly, operation 436 is skipped over (notperformed) in some approaches.

Method 400 further includes sending one or more instructions to storethe second copy of the inode entry after an identifier in the alternatelast block of storage space. See operation 438. In some approaches, thesecond copy of the inode entry may include the same metadata as thefirst copy of the inode entry. Accordingly, the second copy is acondensed version of the entry in the central inode list. However, inother approaches the second copy of the inode entry may include more orless metadata than the first copy of the inode entry, e.g., depending onan amount of available storage space in the tail region of theidentified block.

Further still, operation 440 includes sending one or more instructionsto store a timestamp which corresponds to the second copy of the inodeentry. As mentioned above, timestamps are used in some situations todistinguish between more than one copy of the same inode list entry.Accordingly, any of the approaches described above with respect tooperation 422 may be implemented in order to perform operation 440,e.g., as would be appreciated by one skilled in the art after readingthe present description.

From operation 440, the flowchart of FIG. 4B proceeds to operation 442,whereby method 430 may end. Similarly, method 430 jumps to operation 442from decision 432 in response to determining that the data included inthe received write request does not have a high priority associatedtherewith. However, it should be noted that although method 430 may endupon reaching operation 442, any one or more of the processes includedin method 430 may be repeated in order to determine whether additionalwrite requests include data having a high priority.

Over time the data included in files of a filesystem, as well as therelationships which exist between the files, change as new writerequests, delete requests, file updates, etc., are performed by thefilesystem. Accordingly, the central inode list is updated over time aswell. Copies of the entries in the central inode list are alsopreferably updated in a timely fashion such that they reflect changes insize of the various files stored in memory, and provide a viablerepresentation of the central inode list. For instance, looking to FIG.4C, processes of a method 450 which may be used to supplement method 400and/or method 430 are illustrated in accordance with an exemplaryapproach. The various processes in method 450 are implemented in thebackground in preferred approaches, e.g., such that they may beimplemented at any point during operation of method 400 withouteffecting performance thereof. However, it should be noted that thesupplemental processes of FIG. 4C are illustrated in accordance with oneembodiment which is in no way intended to limit the invention.

As shown, operation 452 involves monitoring a frequency at which thedata that corresponds to the entries in the central inode list isupdated. In some approaches, the update frequency of a given grouping ofdata (e.g., file) is determined using a temperature of the data. Withrespect to the present description, the “temperature” or “heat” of datarefers to the rate (e.g., frequency) at which the data is updated (e.g.,rewritten with new data). Blocks of storage space considered as having ahigh temperature or as being hot tend to have a frequent updated rate,while memory blocks that have a low temperature or which are consideredas being cold have a slower update rate, at least with respect to theupdate rate of hot blocks.

Decision 454 further includes using the frequency at which the data isupdated to determine whether to update the copy of the inode entry. Insome approaches, the determination made in decision 454 uses informationwhich corresponds to a last time a given copy of an inode entry wasupdated, e.g., to determine whether updating the copy of the inode entryis desired.

In response to determining that the copy of the inode entry should beupdated, method 450 proceeds to operation 456 which includes sending oneor more instructions to update the copy of the inode entry. The processof updating the copy of the inode entry may include performing any ofthe same or similar operations as those implemented to originally createthe copy of the inode entry. Accordingly, any of the approachesdescribed above in correlation with operation 414 may be implemented toupdate the copy of the inode entry, e.g., as would be appreciated by oneskilled in the art after reading the present description.

From operation 456, the flowchart of FIG. 4C proceeds to operation 458,whereby method 450 may end. Similarly, method 450 jumps to operation 458from decision 454 in response to determining that the copy of the inodeentry should not be updated. However, it should be noted that althoughmethod 450 may end upon reaching operation 458, any one or more of theprocesses included in method 450 may be repeated in order to determinewhether additional inode entry copies should be updated.

As mentioned above, a loss of the central inode list undesirably causesthe entire filesystem to essentially become useless, as there is no wayof identifying where each file begins, much less where each of thevarious blocks that belong to that file reside throughout the memory. Inother words, without the central inode list, the information stored inmemory essentially becomes an indecipherable string of logical “1s” and“0s”. Accordingly, the distributed copies of the entries in the centralinode list as described in the various approaches herein may be used toreconstruct the central inode list, e.g., after becoming inaccessible.Moreover, the manner in which the distributed copies of the inode listentries are implemented does not consume otherwise usable storage space,and therefore has no detrimental impact on storage capacity which hasnot been conventionally achievable.

Looking now to FIG. 5, a method 500 for reconstructing a central inodelist and filesystem is illustrated in accordance with one embodiment.The method 500 may be performed in accordance with the present inventionin any of the environments depicted in FIGS. 1-4C, among others, invarious approaches. For example, method 500 may be running in thebackground (e.g., unbeknownst to a user) such that various ones of theprocesses included in method 500 are performed in response toexperiencing a disaster situation in order to successfully recover thecentral inode list. Of course, more or less operations than thosespecifically described in FIG. 5 may be included in method 500, as wouldbe understood by one of skill in the art upon reading the presentdescriptions. Moreover, some or all of the operations of the method 500may be combined with some or all operations of the other figures, e.g.,FIGS. 4A-4C, in any combination in various embodiments.

Each of the steps of the method 500 may be performed by any suitablecomponent of the operating environment. For example, in variousapproaches, the method 500 may be partially or entirely performed by acontroller, a processor, a computer, etc., or some other device havingone or more processors therein. Furthermore, the controller, processor,computer, etc., used to perform various ones of the processes in method500 is electrically coupled to a memory in preferred approaches. Thus,in some approaches, method 500 is a computer-implemented method.Moreover, the terms computer, processor and controller may be usedinterchangeably with regards to any of the approaches herein, suchcomponents being considered equivalents in the many various permutationsof the present invention.

Moreover, for those approaches having a processor, the processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method500. Illustrative processors include, but are not limited to, a centralprocessing unit (CPU), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), etc., combinationsthereof, or any other suitable computing device known in the art.

As shown in FIG. 5, operation 502 of method 500 includes detecting adisaster situation in which the central inode list is inaccessible(e.g., unrecoverable). Moreover, operation 504 includes scanning all thebits of information stored in each of the multiple blocks of memory fromstart to finish. In other words, a data storage component (e.g.,magnetic read head, memory I/O unit, etc.) which is able to read bits ofinformation from the physical medium on which the blocks of data arestored, reads each of the bits stored on the physical medium. Accordingto some approaches, the “start” corresponds to data stored in a firstphysical storage location, while the “finish” corresponds to data storedin a last physical storage location. In one example, which is in no wayintended to limit the invention, the “start” corresponds to data storedin a first block of an outermost track on a disk, while the “finish”corresponds to data stored in a last block of an innermost track on thedisk. In other approaches, the “start” corresponds to data stored in afirst logical position (e.g., LBA), while the “finish” corresponds todata stored in a last logical position.

While scanning all the bits of information stored in each of themultiple blocks of memory from start to finish, the data storagecomponent is preferably searching for the various identifiers (e.g.,magic strings) scattered among the bits of information. As mentionedabove, each of the identifiers are preferably constructed such that theyare easily identifiable and therefore distinguishable from the remainderof the bits of information. Accordingly, operation 506 includesdetecting each of the identifiers included in the information. Moreover,each of the detected identifiers are used to locate a corresponding copyof an inode entry from among the numerous bits of information in memory.See operation 508.

It follows that the metadata included in each of the located inode entrycopies can be used to reconstruct the central inode list using anyprocesses which would be apparent to one skilled in the art afterreading the present description. In some approaches the metadata isduplicated from each of the located inode entry copies and used toconstruct a new version of the central inode list. In other approaches,the metadata extracted from the located inode entry copies is used torebuild (e.g., repair) the inaccessible central inode list. Moreover,the central inode list may be reconstructed in the same or differentmemory as the inaccessible central inode list.

However, more than one copy of a given inode entry may exist in theinformation. As mentioned above, certain circumstances may trigger thestorage of more than one copy of the same inode entry in the tailregions of the blocks. For example, at least two copies of an inodeentry corresponding to data determined as having a high priorityassociated therewith is stored in different blocks of storage space atthe end of the respective files. Accordingly, a most updated andaccurate one of the multiple copies of the same inode entry ispreferably used to locate the data which corresponds thereto. Looking todecision 510, a determination is first made as to whether any two ormore of the located inode entry copies have timestamps correspondingthereto. The presence of more than one inode entry copy with a timestampcorresponding thereto indicates that more than one copy of the sameinode entry was created.

Accordingly, method 500 proceeds to operation 512 in response todetermining that two or more of the located inode entry copies do havetimestamps corresponding thereto. There, operation 512 includes usingthe timestamps to deduplicate the more than one copy of a same inodeentry. In one approach, the deduplication process involves identifyingthe most recent (e.g., up-to-date) timestamp and disregarding theremaining timestamps. Moreover, the inode entry copy corresponding tothe timestamp identified as being the most recent is further used tolocate data, e.g., as will soon become apparent.

Again, the copies of the inode entries can also be used to reconstructthe general body of the filesystem altogether. Accordingly, each of thelocated inode entry copies are used to locate the data which correspondsthereto. See operation 514. In other words, each of the inode entrycopies are used to identify the data included in the block or file whichcorresponds to the given copy of the inode entry. According to someapproaches, each of the located inode entry copies are extracted fromthe remainder of the information stored in the memory and the metadataincluded there is examined in order to locate the data (e.g., file orportion of a file) which corresponds thereto. This may be accomplishedregardless of whether the inode entry copy has direct access to thecorresponding block of storage space (e.g., direct block), or anindirect relationship (indirect block). Moreover, the data whichcorresponds to a given inode entry copy may be identified differentlydepending on the approach. For instance, in some approaches the datawhich corresponds to a given inode entry copy is identified bydetermining the LBA which corresponds thereto, which in turn may be usedto locate the specific data or block in which the data is stored.

Operation 516 further includes copying the located data to a secondmemory. According to the present description, “second memory” is in noway intended to be limiting and may include a separate storage drive, adifferent tier of a multi-tiered data storage system, a differentphysical storage location (e.g., a different track on a magnetic disk),etc., which is removed from the one in which the failed central inodelist and corresponding data is located. In some approaches the secondmemory may be selected such that it is the same or similar type ofmemory as the data's previous storage location. In other approaches, thesecond memory may be selected such that it is a different type of memorythan the data's previous storage location.

Upon copying all of the located data to the second memory andestablishing a new central inode list, the filesystem may transfer tothe second memory in the background. As a result, a user will regainaccess to the filesystem and the data stored thereon, e.g., such thatnormal storage operations may resume. Thus, even in situations in whichthe central inode list is lost, operation of the filesystem ismaintained by the various processes included in method 500 which areable to replicate the lost inode list and the filesystem itself. Again,this is made possible by implementing and maintaining a distributed copyof the central inode list in such a way that does not consume storagespace which is otherwise usable. Thus, by scanning the memory (e.g.,disk, LUN, volume, etc.) from start to finish, the magic strings areeasily identifiable. Moreover, each of these magic strings identifies acopy of an inode entry which is able to assist in recovering a specificfile, thereby allowing for all data to be recovered onto anotherfilesystem. Furthermore, this is achievable regardless of whether aredundant backup of the central inode list already exists elsewhere instorage and/or how recently such a backup has been updated.

From operation 516, the flowchart of FIG. 5 proceeds to operation 518,whereby method 500 may end. However, it should be noted that althoughmethod 500 may end upon reaching operation 518, any one or more of theprocesses included in method 500 may be repeated in order to react toadditional disaster situations.

It follows that various ones of the approaches described herein aredesirably able to replicate entries in the central inode list such thatno otherwise usable storage space is consumed in doing so. This isachieved by storing a copy of an inode entry in the tail region of theblock of storage space found at the end of the corresponding file.Again, the tail regions of unused storage space in various blocks at theend of files are otherwise not utilized during the data storage process.Thus, storing copies of inode entries in these tail regions has nodetrimental impact on the overall storage capacity of the memory.

The magic string structures can also be searched for in the event of adata loss (e.g., disaster) situation where the central inode list islost, thereby also minimizing the resulting write amplification.Distributing these inode entry copies across the various blocks ofstorage space also desirably reduces the exposure to a total data loss.Even in the event that the central inode list becomes inaccessible, theapproaches included herein remain resistant to a total loss of theinformation included in the inode list. For example, while some blocksof storage space in memory may fail or otherwise become inaccessible,the inode entry copies included therein are only a small portion of thetotal number of inode entry copies which are distributed across thevarious blocks of storage space. Moreover, even if all copies of a giveninode entry and/or the corresponding indirect block is lost, only therespective file is lost rather than all files in the filesystem as wouldbe experienced in conventional implementations.

Again, the storage architectures achieved by the various approachesincluded herein are able to maintain a distributed copy of the centralinode list which is resilient and which does not consume otherwiseusable storage space. In other words, the various improvements achievedby the various approaches herein come at no storage cost which issignificantly desirable, particularly in view of the shortcomingsexperienced by conventional implementations.

Again, the storage architectures achieved by the various approachesincluded herein are able to maintain a distributed copy of the centralinode list which is resilient and which does not consume otherwiseusable storage space. In other words, the various improvements achievedby the various approaches herein come at no storage cost which issignificantly desirable, particularly in view of the shortcomingsexperienced by conventional implementations.

However, conventional products also experience issues which revolvearound the manner by which a central inode list is actually accessed.For instance, as file systems grow and become larger, multiple processesand/or threads attempt to simultaneously access a single inode list in agiven system. Accordingly, the inode list can become a performancebottleneck and consume valuable system resources, including but notlimited to memory and CPUs. Moreover, lease and lock requests areimplemented per inode in order to access files which undesirably addsanother layer of complexity to the process of accessing data stored inmemory.

Thus, conventional products are inefficient in the way that data islocated and accessed in memory. In sharp contrast, various ones of theapproaches included herein address these performance issues byleveraging locality of reference and implementing techniques which linkaffiliated files together. With reference to the present description,locality of reference refers to the phenomenon in which the same values(e.g., related storage locations), are frequently accessed as reflectedin a memory access pattern. One type of reference locality is temporallocality which refers to the reuse of specific data and/or resourceswithin a relatively small time duration. Accordingly, systems whichexhibit strong locality of reference are desirable candidates forperformance optimization through the use of techniques such as thecaching and prefetching for memory.

It follows that some of the approaches described herein are able toachieve new processes which enable applications and/or threads to accessfiles that are logically linked together by using temporal localitytechniques instead of accessing the mode list to get each and every filelocation. As a result, accessing a central mode list is often bypassed,thereby reducing data processing delays and increasing overallefficiency of the system, e.g., as will be described in further detailbelow.

Referring now to FIG. 6A, a method 600 for accessing specific data whilealso bypassing a central mode list is illustrated in accordance with oneembodiment. The method 600 may be performed in accordance with thepresent invention in any of the environments depicted in FIGS. 1-5,among others, in various approaches. For example, method 600 may berunning in the background (e.g., unbeknownst to a user) such thatvarious ones of the processes included in method 600 are performed inresponse to experiencing a disaster situation in order to successfullyrecover the central mode list. Of course, more or less operations thanthose specifically described in FIG. 6A may be included in method 600,as would be understood by one of skill in the art upon reading thepresent descriptions.

Each of the steps of the method 600 may be performed by any suitablecomponent of the operating environment. For example, in variousapproaches, the method 600 may be partially or entirely performed by acontroller, a processor, a computer, etc., or some other device havingone or more processors therein. Furthermore, the controller, processor,computer, etc., used to perform various ones of the processes in method600 is electrically coupled to a memory in preferred approaches. Thus,in some approaches, method 600 is a computer-implemented method.Moreover, the terms computer, processor and controller may be usedinterchangeably with regards to any of the approaches herein, suchcomponents being considered equivalents in the many various permutationsof the present invention.

Moreover, for those approaches having a processor, the processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method600. Illustrative processors include, but are not limited to, a centralprocessing unit (CPU), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), etc., combinationsthereof, or any other suitable computing device known in the art.

As shown in FIG. 6A, operation 602 of method 600 includes receiving anaccess request for data in at least a first block of storage space inmemory. In some approaches, the data specified in the access requestcorresponds to a specific file or other unique grouping of data (e.g.,such as an object). Accordingly, the requested data may be stored inmore than one block of storage space. Moreover, the access request maybe received from a number of different locations depending on theapproach. For instance, in some approaches the access request is a readrequest received directly from a user. In other approaches the accessrequest is received from an application which is currently operating(e.g., active).

Operation 604 further includes accessing the data in the at least firstblock of storage space, while operation 606 includes returning the datain the at least first block of storage space in response to the accessrequest. In other words, once the requested data is accessed frommemory, it is preferably used to satisfy the received request.

Although the data access request received in operation 602 may besatisfied, method 600 includes additional processes which are able toanticipate additional requests and prepare accordingly. As a result,overall processing delays are reduced and efficiency of the system as awhole improves. Moreover, this is achieved without referencing a centralinode list, thereby further improving data access rates.

Looking to operation 608, method 600 additionally includes locating anidentifier at an end of the data in the first block of storage spaceused to satisfy the data access request. As mentioned above, certainpages in memory include identifiers which identify the boundary betweendata and metadata stored therein. Moreover, each of these identifiersare created in a tail region of the respective block having availablestorage space which would otherwise not be used. According to anillustrative approach, the last page in a given block of storage spacewhich is not filled to capacity (e.g., includes at least some unusedstorage space therein) is used to store the identifier and subsequentmetadata. In other words, the identifiers and corresponding metadata donot consume storage space which would otherwise be available to storedata therein. As a result, implementing the identifiers andcorresponding metadata does not decrease the usable storage capacity ofmemory. Moreover, the metadata which follows the identifier in a givenblock of storage space is included in a trailer in some approaches.Accordingly, a trailer may be appended to the identifier and used tostore any metadata included in the tail region of the block in variousapproaches.

As mentioned above, while the metadata preferably corresponds to thedata stored in the respective block of storage space, the type(s) ofmetadata included in the trailer of a given block varies depending onthe approach. For example, in some approaches the metadata in a trailerof a given block includes a copy of an inode entry in a central inodelist which corresponds to the data stored in the given block of storagespace. In other approaches the metadata may include a user-readable nameof the corresponding file, a size of the corresponding file, a level ofimportance associated with the corresponding file, etc.

However, in still further approaches, the trailers in some blocks ofstorage space include pointers which reference specific data (e.g.,files) and/or the blocks in which the specific data is stored. In suchapproaches, the pointers may follow (e.g., come after) any metadatawhich is in the respective trailer of the block, but are in no waylimited thereto. These pointers serve as links which may be establishedbetween blocks of storage space, e.g., based on the connections whichexist between the data (e.g., files) stored therein. For instance,“locality of reference” refers to the phenomenon in which the samevalues, or related storage locations, are frequently accessed, e.g.,depending on a memory access pattern. One type of reference locality istemporal locality which refers to the reuse of specific data and/orresources within a relatively small time duration.

Accordingly, access patterns are detected and examined in variousapproaches in order to determine locality of reference between two ormore files which are repeatedly accessed at about the same time,accessed in succession, accessed in response to a predeterminedcondition being met, etc. Pointers which link multiple files and/or theblocks in which the files are stored in the tail regions by theoperating system which actually wrote the files in some approaches.

It follows that any pointers in the trailer of a first block of storagespace can be used to identify other blocks of storage space whichinclude data that is typically accessed along with the data in the firstblock. Said another way, any pointers in the trailer of a first block ofstorage space can be used to identify other blocks of storage spacewhich include data that is at least somewhat related to the dataincluded in the first block. Accordingly, operation 610 further includesusing pointers included in a trailer appended to the identifier toidentify additional blocks of storage space which include data havingtemporal locality with the data in the first block of storage space.

However, the relevancy of the pointers included in a given trailer ortail region is also preferably determined before use. In someapproaches, system usage dynamics are used to determine the relevancy ofvarious pointers. For example, files which have expanded (e.g., grown insize) since a time that one or more pointers were formed to pointthereto likely will have overwritten at least a portion of the tailregions of the blocks in which the files are stored. Accordingly,pointers included in these expanded blocks and/or which point theretowill likely be corrupted, thereby prompting the system to fetch anyrelevant metadata from the central inode list itself. Similarly, filesthat have reduced in size due to modifications will also cause anypointers pointing thereto to become obsolete. Accordingly, it ispreferred that the system monitors each block and/or page that is loadedto recognize any updates (e.g., changes) to the tail region.

Systems that exhibit strong locality of reference are also desirablecandidates for performance improvements through the use of techniquessuch as caching and prefetching for memory, as doing so reduces overalldata access times, processing delays, request response times, etc.Moreover, efficiency of the storage as a whole is increasedsignificantly. Thus, upon identifying any additional blocks of storagespace which include data having temporal locality with the data in thefirst block of storage space, the data in each of the identifiedadditional blocks of storage space is prepared for use. See operation612. According to the present description, “prepared for use” isintended to signify that preliminary steps are taken to access the datain each of the identified additional blocks of storage space inpreparation for an actual request to do so. It follows that thepreparation performed in operation 612 makes this data which hastemporal locality with the data in the first block of storage space moreeasily accessible. As mentioned above, this significantly improvesperformance.

Depending on the approach, the process of actually preparing the data ineach identified additional blocks of storage space for use varies. Forinstance, looking to FIG. 6B, exemplary sub-processes of preparing thedata in each identified additional blocks of storage space for use areillustrated in accordance with one embodiment, one or more of which maybe used to perform operation 612 of FIG. 6A. However, it should be notedthat the sub-processes of FIG. 6B are illustrated in accordance with oneembodiment which is in no way intended to limit the invention.

As show, the flowchart of FIG. 6B includes prefetching the data in eachof the identified additional blocks of storage space. See sub-operation620. The data can be prefetched using any processes which would beapparent to one skilled in the art after reading the presentdescription. For instance, in some approaches the data may be prefetchedby performing a mock read operation and creating a copy of the datawhich is read. Moreover, sub-operation 622 includes storing theprefetched data in a specific memory location. This specific memorylocation is preferably more easily (e.g., quickly) accessible than thelocation of the block(s) from which the data was read. In other words,the prefetching performed in sub-operation 622 preferably reduces anaccess time for the respective data. Thus, the prefetched data is storedin high performance memory in preferred approaches. For example, whichis in no way intended to limit the invention, the prefetched data isstored (e.g., copied to) RAM.

However, looking to FIG. 6C, exemplary sub-processes of preparing thedata in each identified additional blocks of storage space for use areillustrated in accordance with another embodiment, one or more of whichmay be used to perform operation 612 of FIG. 6A. Again, it should benoted that the sub-processes of FIG. 6C are illustrated in accordancewith one embodiment which is in no way intended to limit the invention.

As shown, preparing the data in the identified additional blocks ofstorage space for use includes extracting the metadata from the trailerin each of the identified additional blocks of storage space. Seesub-operation 630. As mentioned above, in some approaches the trailer ineach block of storage space includes metadata which corresponds to thedata stored in the respective block of storage space. This metadata(e.g., such as file name, storage location, file size, etc.) in each ofthe identified additional blocks of storage space may thereby be used toaccess the data identified as having temporal locality with the data inthe first block of storage space more efficiently (e.g., quickly).

Sub-operation 632 further includes storing the extracted metadata in alookup table, e.g., such that the metadata is readily accessible.According to some approaches, the metadata is stored in a metadata tablewhich is created on the fly by retrieving (e.g., extracting) themetadata off the respective tails as described herein. As a result, thisad-hoc metadata table can desirably be constructed prior to referencingthe central inode list.

Returning to FIG. 6A, method 600 further includes receiving a subsequentaccess request for at least a portion of the data in the identifiedadditional blocks of storage space. See operation 614. In other words,operation 614 includes receiving an access request for the dataidentified as having temporal locality with the data in the first blockof storage space. Moreover, operation 616 includes returning the atleast a portion of the data in the identified additional blocks ofstorage space in response to the subsequent access request. Accordingly,the preparations made in operation 612 desirably allow for thesubsequently requested data to be retrieved and provided more quicklyand efficiently, thereby consuming fewer system resources, e.g., such ascomputing power. The subsequently requested data is also desirablyreturned without consulting a central inode list thereby furtherreducing data access times and improving system performance efficiency.

While it is preferred that the subsequent access request is received inoperation 612 such that the preparations (e.g., prefetching) performedin operation 610 is actually benefited from, it should be noted that asubsequent access request specifying the data identified as havingtemporal locality with already requested data is not received in everysituation. Accordingly, data that has been prepared for subsequentaccess may be maintained in a prepared state for a predetermined amountof time, until a next data access request is received, unless apredetermined condition has been met, until one or more instructions arereceived from a user, etc., e.g., depending on the desired approach.

However, it should be noted that not all blocks of storage space includean identifier as described above. Accordingly, in some approachesoperation 608 may not be able to locate an identifier at an end of thedata in the first block of storage space. In such approaches, a centralinode list may be accessed in order to identify the additional blocks ofstorage space which include data that is correlated to the data in thedata access request. Upon identifying the additional blocks of storagespace using the central inode list, any one or more of the approachesincluded herein may be implemented in order to preparing the data ineach of the identified additional blocks of storage space for use, e.g.,as would be appreciated by one skilled in the art after reading thepresent description.

Although not depicted in FIG. 6A, method 600 may return to operation 602from operation 616, e.g., such that any one or more of the processesincluded in FIG. 6 are repeated for another received access request.However, method 600 may alternatively return to operation 602 fromoperation 612 in some approaches, e.g., in response to not receiving anaccess request for the data identified as having temporal locality withthe data in the first block of storage space.

Again, certain combinations of files stored in memory are accessed withsome level of repetition. Accordingly, certain files establish a levelof temporal locality with each other. Moreover, various ones of theembodiments included herein are able to access files that are logicallylinked together by utilizing temporal locality techniques rather thanaccessing a central inode list in order to determine storage locationsof such files. As a result, some of the embodiments herein are able tosignificantly reduce data access times, system delay, consumption ofcomputational resources, etc.

These improvements are also achieved without reducing the effectivestorage capacity of the system which further extends the significance ofthe achievements described herein. By implementing the relevant metadataand pointers in the storage space of tail regions of blocks which wouldotherwise go unused, the approaches included herein have no detrimentalimpact on the overall storage capacity of the memory. The magic stringstructures can also be searched for in the event of a data loss (e.g.,disaster) situation where the central inode list is lost, thereby alsominimizing the resulting write amplification, e.g., according to any ofthe approaches included herein.

It should also be noted that any one of the approaches included hereinmay be applied to all files stored in memory, or only certain files,e.g., depending on the desired approach. For instance, in someapproaches a trailer (e.g., tail region) is formed or updated on theblocks of storage space corresponding thereto each time the file ismodified. However, in other approaches a trailer is formed or updatedfor files designated as having a high level of importance, specified bya user, which meet certain criteria, etc.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a LAN or a WAN, or the connection may be madeto an external computer (for example, through the Internet using anInternet Service Provider). In some embodiments, electronic circuitryincluding, for example, programmable logic circuitry, field-programmablegate arrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. The processor may be of any configuration as describedherein, such as a discrete processor or a processing circuit thatincludes many components such as processing hardware, memory, I/Ointerfaces, etc. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a FPGA, etc. By executable by theprocessor, what is meant is that the logic is hardware logic; softwarelogic such as firmware, part of an operating system, part of anapplication program; etc., or some combination of hardware and softwarelogic that is accessible by the processor and configured to cause theprocessor to perform some functionality upon execution by the processor.Software logic may be stored on local and/or remote memory of any memorytype, as known in the art. Any processor known in the art may be used,such as a software processor module and/or a hardware processor such asan ASIC, a FPGA, a central processing unit (CPU), an integrated circuit(IC), a graphics processing unit (GPU), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A computer-implemented method, comprising:receiving an access request for data in a first block of storage spacein memory; returning the data in the first block of storage space inresponse to the access request thereby satisfying the access request; inresponse to satisfying the access request, locating an identifier at anend of the data in the first block of storage space; using pointersincluded in a trailer appended to the identifier to identify additionalblocks of storage space which include data having temporal locality withthe data in the first block of storage space; and preparing the data ineach of the identified additional blocks of storage space for use. 2.The computer-implemented method of claim 1, wherein preparing the datain the identified additional blocks of storage space for use includes:prefetching the data in each of the identified additional blocks ofstorage space by performing a mock read operation; storing theprefetched data in random access memory; receiving a subsequent accessrequest for at least a portion of the prefetched data in the randomaccess memory, wherein the subsequent access request is different fromthe access request for the data in the first block; and returning the atleast a portion of the prefetched data from the random access memory inresponse to the subsequent access request without consulting a centralinode list.
 3. The computer-implemented method of claim 1, wherein thetrailer in each block of storage space includes metadata whichcorresponds to the data stored in the respective block of storage space.4. The computer-implemented method of claim 3, wherein preparing thedata in the identified additional blocks of storage space for useincludes: extracting the metadata from the trailer in each of theidentified additional blocks of storage space; and storing the extractedmetadata in a lookup table.
 5. The computer-implemented method of claim3, wherein the metadata includes a copy of a first inode entry in acentral inode list which corresponds to the data stored in therespective block of storage space, wherein the metadata includes a copyof a second inode entry in the central inode list which corresponds todata that is different than the data stored in the respective block ofstorage space.
 6. The computer-implemented method of claim 1,comprising: receiving a subsequent access request for at least a portionof the data in the identified additional blocks of storage space,wherein the subsequent access request is different from the accessrequest for the data in the first block; and returning the at least aportion of the data in the identified additional blocks of storage spacein response to the subsequent access request without consulting acentral inode list.
 7. The computer-implemented method of claim 1,comprising: detecting a disaster situation in which a central inode listis inaccessible; scanning information stored in each block of storagespace in the memory; detecting each identifier included in theinformation; using each of the detected identifiers to locate acorresponding copy of an inode entry in the information; using each ofthe located inode entry copies to locate data in the information whichcorresponds thereto; and copying the located data to a second storage.8. A computer program product comprising a computer readable storagemedium having program instructions embodied therewith, wherein thecomputer readable storage medium is not a transitory signal per se, theprogram instructions readable and/or executable by a processor to causethe processor to perform a method comprising: receiving, by theprocessor, an access request for data in a first block of storage spacein memory; returning, by the processor, the data in the first block ofstorage space in response to the access request; locating, by theprocessor, an identifier at an end of the data in the first block ofstorage space; using, by the processor, pointers included in a trailerappended to the identifier to identify additional blocks of storagespace which include data having temporal locality with the data in thefirst block of storage space; preparing, by the processor, the data ineach of the identified additional blocks of storage space for use;detecting, by the processor, a disaster situation in which a centralinode list is inaccessible; scanning, by the processor, informationstored in each block of storage space in the memory; detecting, by theprocessor, each identifier included in the information; using, by theprocessor, each of the detected identifiers to locate a correspondingcopy of an inode entry in the information; using, by the processor, eachof the located inode entry copies to locate data in the informationwhich corresponds thereto; and copying, by the processor, the locateddata to a second storage.
 9. The computer program product of claim 8,wherein preparing the data in the identified additional blocks ofstorage space for use includes: prefetching the data in each of theidentified additional blocks of storage space; and storing theprefetched data in random access memory.
 10. The computer programproduct of claim 8, wherein the trailer in each block of storage spaceincludes metadata which corresponds to the data stored in the respectiveblock of storage space.
 11. The computer program product of claim 10,wherein preparing the data in the identified additional blocks ofstorage space for use includes: extracting the metadata from the trailerin each of the identified additional blocks of storage space; andstoring the extracted metadata in a lookup table.
 12. The computerprogram product of claim 10, wherein the metadata includes a copy of afirst inode entry in a central inode list which corresponds to the datastored in the respective block of storage space, wherein the metadataincludes a copy of a second inode entry in the central inode list whichcorresponds to data that is different than the data stored in therespective block of storage space.
 13. The computer program product ofclaim 8, the program instructions readable and/or executable by aprocessor to cause the processor to perform the method comprising:receiving, by the processor, a subsequent access request for at least aportion of the data in the identified additional blocks of storagespace, wherein the subsequent access request is different from theaccess request for the data in the first block; and returning, by theprocessor, the at least a portion of the data in the identifiedadditional blocks of storage space in response to the subsequent accessrequest without consulting a central inode list.
 14. A system,comprising: a processor; and logic integrated with the processor,executable by the processor, or integrated with and executable by theprocessor, the logic being configured to: receive, by the processor, anaccess request for data in a first block of storage space in memory;return, by the processor, the data in the first block of storage spacein response to the access request, thereby satisfying the accessrequest; locate, by the processor, an identifier at an end of the datain the first block of storage space in response to satisfying the accessrequest; use, by the processor, pointers included in a trailer appendedto the identifier to identify additional blocks of storage space whichinclude data having temporal locality with the data in the first blockof storage space; and prepare, by the processor, the data in each of theidentified additional blocks of storage space for use.
 15. The system ofclaim 14, wherein preparing the data in the identified additional blocksof storage space for use includes: prefetching the data in each of theidentified additional blocks of storage space by performing a mock readoperation; storing the prefetched data in random access memory;receiving a subsequent access request for at least a portion of theprefetched data in the random access memory, wherein the subsequentaccess request is different from the access request for the data in thefirst block; and returning the at least a portion of the prefetched datafrom the random access memory in response to the subsequent accessrequest without consulting a central inode list.
 16. The system of claim14, wherein the trailer in each block of storage space includes metadatawhich corresponds to the data stored in the respective block of storagespace.
 17. The system of claim 16, wherein preparing the data in theidentified additional blocks of storage space for use includes:extracting the metadata from the trailer in each of the identifiedadditional blocks of storage space; and storing the extracted metadatain a lookup table.
 18. The system of claim 16, wherein the metadataincludes a copy of a first inode entry in a central inode list whichcorresponds to the data stored in the respective block of storage space,wherein the metadata includes a copy of a second inode entry in thecentral inode list which corresponds to data that is different than thedata stored in the respective block of storage space.
 19. The system ofclaim 14, the logic being configured to: receive, by the processor, asubsequent access request for at least a portion of the data in theidentified additional blocks of storage space, wherein the subsequentaccess request is different from the access request for the data in thefirst block; and return, by the processor, the at least a portion of thedata in the identified additional blocks of storage space in response tothe subsequent access request without consulting a central inode list.